Modern data handling and storage devices, such as disc drives, are commonly used in a multitude of computer environments to store large amounts of data in a form that is readily available to a host computer. Generally, a disc drive has a magnetic disc, or two or more stacked magnetic discs, that are rotated by a motor at high speed. Each disc typically has two data storage surfaces each divided into a series of generally concentric data tracks where data is stored in the form of magnetic flux transitions.
A data transfer member such as a magnetic transducer or “head” is moved by an actuator arm to selected positions adjacent the data storage surface to sense the magnetic flux transitions in reading data from the disc, and to transmit electrical signals to induce the magnetic flux transitions in writing data to the disc. The active elements of the data transfer member, such as magnetoresistive head element and an interactive write element, are supported by a suspension structure extending from the actuator arm. The active elements fly at a height slightly above the data storage surface upon an air bearing generated by air currents caused by the spinning discs.
A continuing trend in the industry is toward ever-increasing data storage capacity and processing speed while maintaining or reducing the physical size of the disc drive. Consequently, the data transfer member and supporting structures are continually being miniaturized, and data storage densities are continually being increased. The result is an overall increased sensitivity to excitation both from external sources and from self-excitation sources, which adversely affect the positioning control systems moving the actuator relative to the spinning discs.
One such source of excitation results from air currents moving within the disc stack and impinging on disc drive components. Kinetic energy of the rotating discs is transferred by a shearing action through the boundary layer at the air/disc interface to impart movement to air mass within the disc stack, thereby inducing air currents. The air currents generally spiral outwardly, as the disc rotation imparts a rotational force component and as centrifugal force imparts a radial force component. The velocity is related to the radial location; that is, air moving near the disc axis of rotation moves relatively slowly, and is more likely a laminar flow. As the radial distance from the axis of rotation increases, the currents move faster and become more likely a turbulent flow. In either case, when the currents impinge upon an object, such as the data transfer member and/or the actuator, turbulence is likely. Turbulence can impart adverse vibrations, or aerodynamic excitation, to the discs (flutter) and/or to the actuator, particularly to the suspension members (buffeting). Turbulence can also be created by shedding vortices action on the actuator as the currents flow past the actuator, and acting on the disc as the currents are expelled from the disc stack.
Disc stacks are also becoming used is in servo-writing operations where discs are written with servo data before the discs are placed into a head-disc assembly. To increase throughput from such servowriting operations, the number of discs placed on a disc stack is being increased. Also, as data density on the discs increases, more precise control of the disc stack during write operations is required. Because the quality of the data written to the discs depends, in part, on the position stability of the write heads as they fly over the disc surfaces, there is a need for a method and device to reduce turbulence in the vicinity of the write elements and the assemblies on which the write elements are carried. The present invention, described below, provides a solution to this and other problems, and offers other advantages over the prior art.